1. Field of the Invention
Priority is claimed on Japanese Patent Application No. 2003-126317, filed May 1, 2003, the content of which is incorporated herein by reference.
The present invention relates to a technology for forming a thin film using a liquid material, and, in particular, to a coating apparatus, a thin film forming method, a thin film forming apparatus, a semiconductor device manufacturing method, an electro-optic device, and to an electronic instrument.
2. Description of Related Art
Conventionally, semiconductor devices employed in various types of electronic instrument are typically formed by thin films such as a semiconductor film, an insulating film, and a conducting film. In the formation of these films, a chemical vapor deposition (CVD) method and a sputtering method are mainly used. CVD methods include normal pressure CVD, low pressure CVD, plasma CVD, and optical CVD. Sputtering methods include an AC type and a DC type. An AC type is used for forming an insulating film, while a DC type is used for forming a conducting film.
In conventional CVD methods and sputtering methods, a vacuum apparatus, a power supply unit for generating plasma and the like, a gas supply apparatus for thin film formation, and control of a substrate temperature and the like are necessary. Moreover, the gas used in thin film formation is often toxic, flammable, and prone to spontaneous ignition. Consequently, a variety of ancillary equipment is necessary to ensure safety such as gas leak detectors, noxious substance removal apparatuses for rendering exhaust gas harmless, and exhaust systems in gas containers and gas pipe sections. Accordingly, conventional thin film formation apparatuses have the drawback of being high in cost and large in size. There are also an extremely large number of apparatus conditions contributing to the control of film thickness and film quality, so that conventional thin film formation apparatuses have the drawback that it is difficult to ensure uniformity and reproducibility. Furthermore, in these methods, because a solid phase thin film is formed from a gas phase, conventional thin film formation apparatuses have the drawback of poor productivity. In recent years, methods of manufacturing semiconductor devices and the like in which thin films are formed using methods that are different from the above conventional film formation methods have been proposed as methods for solving the above described problems.
For example, one method involves forming a desired thin film by forming a coating film by coating a liquid material on a substrate, and then heat processing the coating film. The basic thin film formation steps include a coating step in which a coating film is formed by coating a liquid material on a substrate, and a heat processing step for obtaining a desired thin film by performing heat processing on the coating film. According to these steps, a thin film can be formed at low cost and with a high degree of productivity using a small size, low cost apparatus. As a result, a low cost thin film device can be manufactured.
Coating methods such as a spin coating method or liquid discharge method (i.e., an inkjet method) are typically used for the coating step. In the spin coating method, for example, a spinner in which the task of attaching and detaching a cover that is required with any change in the processing solutions is simple (see, for example, Japanese Patent Application Unexamined Publication No. 5-154430), and a coating apparatus capable of supplying a coating solution to a substrate being processed with a lid of a rotating container in a closed state (see, for example, Japanese Patent Application Unexamined Publication No. 8-83762) have been proposed. In the inkjet method, an apparatus has recently been proposed (see, for example, Japanese Patent Application Unexamined Publication No. 9-10657) that forms a coating film having excellent uniformity on a substrate being coated by discharging a liquid from micro nozzles of an inkjet head onto the substrate being coated, while causing the substrate being coated and the inkjet head to move relatively between the area on the rotation shaft side and the area furthest therefrom as the substrate being coated and the inkjet head are rotated relatively.
Moreover, for the heat processing step, a method has been proposed in which an insulating film is baked in a kiln whose oxygen concentration has been adjusted to a fixed value or less (see, for example, Japanese Patent Application No. 9-213693). Furthermore, in a series of steps that includes a coating step and a heat processing step, a coating film formation method has been proposed (see, for example, Japanese Patent Application Unexamined Publication No. 11-262720) in which, for example, a coating solution is dripped onto a surface of an object being processed so that the coating solution is spread uniformly over the surface of the object being processed. A portion of this coating solution that is used to form a film seeps onto the bottom surface of the outer edge of the object being processed, and in that state, the object being processed is transported to a decompression drying apparatus and is dried to a certain extent. It then undergoes heat drying.
However, as was shown in the conventional technology, although a thin film forming apparatus that continuously performs a coating step and a heat processing step, and a variety of coating apparatuses and heat processing apparatuses that are used in the various steps have been proposed, further improvements are required in order, particularly, to improve the performance of the coating apparatus and heat processing apparatus, as well as achieve a reduction in both the size and cost thereof, which in turn will bring about an improvement in the performance of the overall thin film forming apparatus as well as achieve a reduction in both the size and cost thereof.
Moreover, some liquid materials used to form a coating film have problems with regard to safety. For example, because the liquid material normally contains an organic solvent, it is flammable. Consequently, as far as possible, metal materials are used for the members constituting the thin film forming apparatus, and no flammable materials such as plastic materials are used at least in the chamber where the coating step is performed. In addition, other measures need to be implemented such as providing a structure for expelling vapor from the organic solvent. It cannot be said, however, that conventional coating apparatuses and thin film forming apparatuses are always formed in this manner.
If the liquid material is one that requires particular care as regards safety, such as liquid materials that generate noxious gas, or that are prone to spontaneous combustion in an oxygen atmosphere, then it has not been possible, essentially, to use such a liquid material in a conventional coating apparatus and thin film forming apparatus.
Furthermore, when forming a semiconductor film or metal film from a liquid material, it is necessary to strictly control the processing atmosphere in the coating and heat processing steps. However, there has not been satisfactory control of the processing atmosphere in conventional thin film forming apparatuses. For example, when forming a Si film, if the coating step and heat processing step are performed in an atmosphere in which even a small amount of oxygen is present, a silicon oxide film ends up being formed in the Si film, resulting in a deterioration in the performance thereof as a semiconductor film. It is necessary in the formation of this type of thin film to control the oxygen concentration to, for example, 10 ppm or less, however, the specific structure required for this has not been proposed conventionally.
Moreover, if the liquid material is left unused for a long period of time, a rise in viscosity and precipitation of solid components is brought about by the volatility of the solvent and chemical reactions and the like. As a result, problems arise such as blockages occurring in the liquid material supply and control systems, and a thin film that contains a large number of defects being formed. In conventional coating apparatuses and thin film forming apparatuses, however, sufficient countermeasures against such problems have not been provided.
The present invention was conceived in view of the above circumstances, and it is an object thereof to provide a coating apparatus, a thin film forming method, a thin film forming apparatus, a semiconductor device manufacturing method, an electro-optic device, and an electronic instrument that enable a high performance thin film with few defects to be obtained, that allow maintenance of the apparatus to be performed efficiently, and that enable a thin film to be formed with a high level of safety.